1. Field of the Invention
The present invention relates to heavy dobbies used for forming the shed in weaving machines of very large width, of the type particularly employed for manufacturing tubular fabrics for the production of endless dryer felts or filters for the paper-making industry.
2. History of the Related Art
Due to the considerable amplitude of the stroke of the heddle frames associated with these dobbies, the conventional open-shed systems cannot be used and closed-shed dobbies must be employed in which each frame moves downwardly or upwardly from a mean position corresponding to the point of crossing of the assembly of the frames.
FIG. 1 of the accompanying drawings schematically shows the general arrangement of the heavy closed-shed dobbies known in practice. Each of the heddle frames CL mounted on the weaving machine is connected by a system of rods 1 to a corresponding oscillating lever 2, articulated at 2a on the fixed frame. One of the ends of each lever 2 is provided with a freely rotatable stop 2b. Each lever is connected with a double rocking hook 3 whose pivoting movement is controlled by pushers (arrows 4) of the reading mechanism of the dobby in order to selectively engage with one or the other of two actuation knives 5. The knives are controlled to move reciprocally in unison in opposite directions.
Actuation of the assembly of the double hooks 3 by the reading mechanism is effected when the two knives 5 lie in a central position (levers 2 oriented vertically) and it will be understood that, depending on whether a hook cooperates with one or the other of the knives 5, the corresponding frame CL moves vertically upwardly or downwardly from the position corresponding to the closure of the shed.
Although such a system functions relatively correctly when the work speed is reduced, this does not apply when the dobby is associated with a weaving machine driven at the high rates now required in practice. In such a case, the double hooks are subjected to the effects of rebound and vibrations which render their engagement by the driving knives random. Furthermore, the pushers 4 have only a very short period of time to act on the double hooks and it happens that the double hooks pivot with a very slight delay. Now, in either case, any defective engagement of one of the double hooks 4 by a knife 5 results in a defect in weaving in the article being made.
It is a principal object of the present invention to overcome these drawbacks.